System and method for multiplexing PDH and packet data

ABSTRACT

A method of efficiently combining data from at least a plurality of a first type of data source and a second type of data source. The method comprises synchronizing the plural first type of data sources to thereby generate a synchronized data rate, providing a frame having plural bit positions, assigning the synchronized first type of data in ones of the bit positions of the frame, and arranging the second type of data in the frame as a function of the synchronized data rate.

BACKGROUND

Digital transmission of signals has become widespread. To this end, avariety of digital transmission media are available which have differenttransmission characteristics and different information capacity. Inorder to make efficient use of the various transmission media, ahierarchy of transmission systems has been developed which operates atdifferent transmission bit rates. In North America, the hierarchyincludes the DS1 signal transmitted at 1.544 Mb/sec, the DS2 signaltransmitted at 6.312 Mb/sec and the DS3 signal transmitted at 44.736Mb/sec on multiple T1 channels. In Europe, a similar but differenthierarchy includes multiple E1 channels transmitted at 2.048 Mb/sec.

The digital signals to be transmitted over a medium enter and leave thedigital hierarchy by means of a signal conversion apparatus. In order togo from one digital transmission rate to a different digitaltransmission rate, one or more multiplexing steps may be required.

For high capacity transmission, it is desirable to efficiently combineor multiplex a plurality of one or more of the digital signals in thehierarchy without the need for intermediate multiplexer (demultiplexer)stages or a number of different multiplexing (demultiplexing) schemes.Additionally, it is equally desirable to efficiently add and/or drop oneor more digital signals of one or more digital transmission bit rateswithout the need for multiple multiplexing and/or demultiplexingprocesses.

There are several known methods utilized to combine or multiplex digitalsignals such as Plesiochronous Digital Hierarchy (PDH), SynchronousDigital Hierarchy (SDH), and asynchronous data with packet data. Somemethods include Asynchronous Transfer Mode (ATM) or mapping the signalsinto a Synchronous Optical Network (SONET) or an SDH frame. Thesemethods are subject to several known problems. For example, in theasynchronous mode, ATM information may be transferred in standard-length53-byte ATM cells. However, the payload transferred on the radio pathdoes not usually measure 48 bytes, i.e. 384 bits, wherefore padding bitsare needed. In addition, if the payload in a block on the radio path islonger than 48 bytes, the content of one block must be transmitted inseveral ATM cells. Thus, ATM mapping generally is not the most efficientmethod of utilizing bandwidth.

Another problem with ATM and SONET/SDH mapping is that the addition ofpadding bits and/or division of the payload between a plural number ofcells adds to the processing of the information to be transferred whenthe transmission network is entered or exited. Such characteristics areundesirable in point-to-point radio applications which require efficientbandwidth utilization and low latency per link.

Thus, a need exists in the art to efficiently combine or multiplexdigital signals, i.e., T1 or E1, having various digital hierarchies withpacket or Ethernet signals for transmission as a single data stream. Itis therefore an object of the present disclosure to provide a novelmethod of transmitting data in a communication system that is adapted toreceive a first type of data having two data streams with differentclocks and a second type of data. The novel method comprises the stepsof receiving data from the first and second types of sources, providinga frame having plural bit positions, synchronizing the received firsttype of data thereby generating a synchronized data rate, assigning thesynchronized first type of data in ones of the bit positions of theframe, distributing the second type of data in ones of the unassignedbit positions as a function of the synchronized data rate, andtransmitting the frame.

It is a further object of the present disclosure to provide a novelmethod for transmitting communication signals in a predetermined frameformat. The novel method comprises the steps of receiving data from aplurality of sources including a first and second type of data source,synchronizing the received first type of data source to thereby generatea synchronized data rate, and transmitting the synchronized first typeof data and received second type of data in a predetermined frame formatwhereby the packet data is assigned in the predetermined frame format asa function of the synchronized data rate.

It is another object of the present disclosure to provide a novel methodwhere data from plural PDH sources and from a packet source arereceived, assigned to bit positions in a frame, and transmitted as asingle data stream whereby the data received from the packet source isarranged in the data stream as a function of a synchronized data rate ofthe received PDH sources.

It is still another object of the present disclosure to provide a novelmethod of combining data from plural first type of data sources and atleast one second type of data source. The novel method comprises thesteps of synchronizing the plural first type of data sources to therebygenerate a synchronized data rate, providing a frame having plural bitpositions, assigning the synchronized first type of data in ones of thebit positions of the frame, and arranging the second type of data in theframe as a function of the synchronized data rate to thereby combinedata from different types of data sources.

It is an object of the present disclosure to provide a novel method oftransmitting data received from plural sources that are not synchronizedwith each other and a packet source as a single data stream. The novelmethod comprises the steps of synchronizing data received from theplural sources that are not synchronized with each other to therebygenerate a synchronized data rate, providing a frame format comprising aplurality of frames each frame having plural sub-frames the number ofwhich correlates to the number of received plural sources that are notsynchronized with each other and each sub-frame comprising a pluralityof blocks, assigning the synchronized data and data received from thepacket source in bit positions of the frame format, and transmitting theassigned data as a single data stream.

It is also an object of the present disclosure to provide a novel systemwhere data from sources having different synchronisms and packet sourcesis transmitted in a frame format as a single data stream the improvementwherein the packet data is arranged in said data stream as a function ofa data rate of said sources having different synchronisms.

These objects and other advantages of the disclosed subject matter willbe readily apparent to one skilled in the art to which the disclosurepertains from a perusal of the claims, the appended drawings, and thefollowing detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a T1/E1 and Ethernet data multiplexeraccording to an embodiment of the present subject matter.

FIG. 2 is an illustration of an exemplary frame format according to anembodiment of the present subject matter.

FIG. 3 is a representative flow chart for the operation of acommunication system according to an embodiment of the present subjectmatter.

FIG. 4 is a representative flow chart for the operation of acommunication system according to another embodiment of the presentsubject matter.

DETAILED DESCRIPTION

The present disclosure is generally directed to a one-step programmabledata multiplex scheme to combine a mixture of standard PlesiochronousDigital Hierarchy (PDH), Synchronous Digital Hierarchy (SDH) andasynchronous data sources such as multiples of E1 and T1 data withpacket data sources for transmission over a medium such as a radio link,cable, fiber or other suitable transmission medium.

With reference to FIG. 1, an embodiment of the present disclosure isillustrated that enables flexible transmission of many differentcapacities of either mixed PDH data and packet data, all PDH data, orall packet data in a given payload capacity. No constraint exists on theembodiment illustrated in FIG. 1 with regard to the data receivedtherein; PDH data is shown for exemplary purposes only and should not beconstrued to limit the disclosure. As shown, all PDH tributaries orsources 1, 2, 3, . . . , N to be multiplexed in a predetermined frameformat having plural sub-frames are synchronized by a synchronizer 11,12, 13, . . . , S_(N). The synchronizers 11, 12, 13, . . . , S_(N) maybe provided with a multiplex synchronous clock 52 or other known clockmeans to produce a synchronized data rate. Several known methods may beutilized to synchronize the PDH source data. For example, the PDH sourcedata may be synchronized by positive bit stuffing. In an embodiment ofthe present disclosure, at least one stuffing opportunity may beassigned to each PDH data source per frame and the stuffing occurrencewill be indicated through stuffing indication bits in its associatedsub-frame. Thus, the stuffing opportunity for PDH₁ is in sub-frame 1,and the stuffing opportunity for PDH₂ is in sub-frame 2, and so on. Whenthe maximum number of PDH data sources is less than that of the numberof sub-frames, the number of stuffing opportunities for each PDH sourceper frame may be increased to improve the jitter performance of acommunication system.

As shown in FIG. 1, Ethernet or packet data is received by multipleports E1, . . . E_(N) such as 10/100 Base-T ports or other suitableports adapted to receive packet data. The ports E1, . . . E_(N) providethe packet data to an Ethernet switch 70 or bridge (not shown). TheEthernet switch 70 may be provided with an Ethernet capacity clock 54having an input from a multiplexer 50 or from another suitable clockmeans. The multiplexer 50 may also be provided with a clock source 56from a master clock or other suitable means. The synchronized data fromthe plurality of PDH data sources are provided to a respective pluralityof data selectors 21, 22, 23, . . . D_(N). Each data selector may alsobe provided with an input from the Ethernet switch 70 thereby providinga packet data input to the plurality of data selectors. It is alsoenvisioned that multiple Ethernet switches may be utilized therebyproviding multiple packet data inputs to the plurality of dataselectors. The data selectors 21, 22, 23, . . . , D_(N) may beprogrammed by software to provide the multiplexer 50 with data fromplural or select sources or exclude plural or select sources.Synchronized PDH data and packet data provided to the multiplexer 50 arearranged in the frame format in the multiplexer 50 which then provides asingle data stream 58 for transmission over a medium. The packet data tobe transmitted is arranged in the frame format to have an integer t(t=1, 2, 3, 4, . . . ) multiple of the synchronized PDH data rate.Although the actual PDH source number to be multiplexed may be limiteddue to practical application purposes, the aggregate payload data rateof the transmitted single data stream 58 using the multiplexing schemeaccording to an embodiment of the present disclosure can be as low as1T1 or 1 E1 to as high as over 100T1 or over 100E1 equivalent capacity.

With reference to FIG. 2, an embodiment of the frame format of thepresent disclosure comprises at least one frame 100 having pluralsub-frames 110. Each sub-frame 110 comprises plural blocks 120 having aplurality of sub-blocks 130. As illustrated, each sub-block 130 includesone bit position for each synchronized PDH source and/or one bitposition for the packet data that is equivalent to the synchronized datarate. Each block 120 within a sub-frame 110 includes n sub-blocks 130,one or more frame complementary overhead bit positions 112, n bitpositions for synchronized data from each PDH source and (t*n) bitpositions for packet data. Any of the n bit positions for thesynchronized data from each PDH source may be filled with packet data ifthe bit positions are not provisioned to carry the synchronized PDHdata. Thus, packet data to be multiplexed may occupy part of all of thebit positions for synchronized PDH data. The synchronized PDH dataand/or packet data may also be sequentially bit interleaved in eachblock or arranged in the frame format by other known suitable sequencingmeans.

For systems having maximum N*PDH data sources with additional t*T1 ort*E1 equivalent packet data rate capacity, there will be n*(N+t) bitpositions for synchronized PDH data and packet data per block. Thus, inthe instance that the total mixed data capacity exceeds the capacitydesignated for the PDH data, additional capacity for packet data may beadded in the increment of t (t=1, 2, 3, 4, . . . ) times thesynchronized PDH (i.e., T1 or E1) rate. As discussed above, this isaccomplished by adding (t*n) bits for the additional packet data perblock in all the blocks of the frame.

As shown in FIG. 2, the frame complementary overhead bit positions 112may contain auxiliary data to be transmitted with the main payload. Thisauxiliary data may be used to carry network management data, servicechannel data and other data. The frame complementary overhead bitpositions 112 may also provide frame house keeping bits such as a FrameAlignment Word (FAW) 114, stuffing indication bits, parity bits andother known housekeeping bits. The stuffing indication bits, parity bitsand other known housekeeping bits may be distributed throughout theframe in unused overhead bit positions 112.

To speed up frame acquisition time, bunched FAW (i.e.,11110110000101000) may be utilized. The FAW 114 would be arranged in thefirst block of the first sub-frame and the frame complementary overheadbit positions 112 designated for the FAW 114 in the sub-frames may befilled with synchronized PDH data bits and/or packet data bits. It isalso envisioned that other housekeeping bits, such as parity bits may beutilized in overhead bit positions of the first sub-frame. The FAW 114may also be distributed in the embodied frame format. In such anembodiment, the FAW bits are distributed in the complementary overheadbit positions 112.

The minimum number of sub-frames 110 required in the frame 100 dependson the maximum number of PDH sources received. For example, if themaximum number of PDH sources is 16, a minimum of 16 sub-frames 110 perframe 100 are used. The number of sub-blocks 130 per block 120 and thenumber of blocks 120 per sub-frame 110 are determined by the requiredcapacity of the auxiliary data, the number of stuffing indication bits(C bits), the number of parity bits, the size of the frame (bits perframe) and/or the available bandwidth in the transmission medium.

With reference to FIG. 3, a representative flow chart is shownillustrating the operation of a communication system according to anembodiment of the present subject matter. A communication system 300 maybe adapted to receive a first type of data having at least two datastreams with different clocks and a second type of data from a first andsecond types of sources, as shown in Block 310. The system 300synchronizes the received first type of data thereby generating asynchronized data rate, as shown in Block 320. A frame format isprovided having plural bit positions, as shown in Block 330. Thesynchronized first type of data are assigned in ones of the bitpositions of the frame while the second type of data are distributed inones of the unassigned bit positions as a function of the synchronizeddata rate, as shown in Block 340. The system 300 then transmits theframe as shown in Block 350.

With reference to FIG. 4, a representative flow chart is shownillustrating for the operation of a communication system according toanother embodiment of the present subject matter. A communication system400 is adaptable to receive data from a plurality of sources including afirst and second type of data source, as shown in Block 410. Thereceived first type of data source is synchronized to thereby generate asynchronized data rate, as shown in Block 420. The synchronized firsttype of data and received second type of data is transmitted in apredetermined frame format whereby the packet data may be assigned inthe predetermined frame format as a function of the synchronized datarate, as shown in Block 430.

While preferred embodiments of the disclosed system and method have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the embodiments of the disclosedsystem and method are to be defined solely by the appended claims whenaccorded a full range of equivalence, many variations and modificationsnaturally occurring to those of skill in the art from a perusal hereof.

1. A method of transmitting data by a communication system comprisingsteps of: receiving first type payload data and second type payloaddata, the first type payload data including two data streamscorresponding to different clocks; synchronizing, with a synchronizer,the received first type payload data thereby generating a synchronizeddata rate; assigning the synchronized first type payload data in bitpositions of a frame; distributing the second type payload data inunassigned bit positions of the frame as a function of the synchronizeddata rate; and transmitting the frame wherein the frame includes pluralsub-frames with plural blocks and sub-blocks, each sub-block including asynchronized first type payload data bit position or a second typepayload data bit position and each block having at least one overheadbit position; inserting a frame alignment word in bit positions of afirst block of the plural blocks and sub-blocks of the first sub-frame;and distributing synchronized first type payload data bits or secondtype payload data bits in unused overhead bit positions of other blocks.2. The method of claim 1 wherein a number of sub-frames correlates to anumber of first type sources.
 3. The method of claim 1 furthercomprising the step of distributing stuffing indication bits in unusedoverhead bit positions.
 4. The method of claim 1 further comprising thestep of distributing parity bits in unused overhead bit positions. 5.The method of claim 1 further comprising the step of: filling inunassigned data bit positions with second type payload data bits.
 6. Themethod of claim 1 wherein the first type payload data includes at leastone of synchronous, asynchronous, and plesiochronous data.
 7. The methodof claim 1 wherein the second type payload data includes a packet data.8. The method of claim 1 wherein the synchronized first type payloaddata and second type payload data is assigned by sequential bitinterleaving.
 9. The method of claim 1 wherein the received first typepayload data is synchronized by bit stuffing.
 10. A method fortransmitting a predetermined frame format by a communication systemcomprising steps of: receiving data from a plurality of sourcesincluding first type payload data from at least one first type datasource and second type payload data from a second type data source;synchronizing, with a synchronizer, the received first type payload datato thereby generate a synchronized data rate; and transmitting thesynchronized first type payload data and received second type payloaddata in a predetermined frame format, wherein the second type payloaddata is assigned in the predetermined frame format as a function of thesynchronized data rate wherein the frame includes plural sub-frames withplural blocks and sub-blocks, each sub-block including a synchronizedfirst type payload data bit position or a second type payload data bitposition and each block having at least one overhead bit position;inserting a frame alignment word in bit positions of a first block ofthe plural blocks and sub-blocks of the first sub-frame; anddistributing synchronized first type payload data bits or second typepayload data bits in unused overhead bit positions of other blocks. 11.The method of claim 10 wherein at least one first type payload dataincludes at least one of synchronous, asynchronous, and plesiochronousdata.
 12. The method of claim 10 wherein the second type payload dataincludes a packet data.
 13. The method of claim 10 further comprisingthe step of sequentially bit interleaving synchronized first typepayload data and second type payload data in the frame format.
 14. Amethod of combining data from plural first type data sources and atleast one second type data source by a communication system comprisingsteps of: synchronizing, with a synchronizer, first type payload datafrom plural first type data sources to thereby generate a synchronizeddata rate; assigning the synchronized first type payload data in bitpositions of a frame; and arranging second type payload data from asecond type data source in the frame as a function of the synchronizeddata rate to thereby combine payload data from different types of datainto the frame wherein the frame includes plural sub-frames with pluralblocks and sub-blocks, each sub-block including a synchronized firsttype data bit position or a second type data bit position and each blockhaving at least one overhead bit position; inserting a frame alignmentword in bit positions of a first block of the plural blocks andsub-blocks of the first sub-frame; and distributing synchronized firsttype payload data bits or second type payload data bits in unusedoverhead bit positions of other blocks.
 15. The method of claim 14further comprising the step of: filling in unassigned bit positions withsecond type payload data bits from a second type data source.
 16. Themethod of claim 14 wherein a number of sub-frames correlates to a numberof received first type sources.
 17. The method of claim 14 furthercomprising the step of distributing stuffing indication bits in unusedoverhead bit positions.
 18. The method of claim 14 further comprisingthe step of distributing parity bits in unused overhead bit positions.19. The method of claim 14 wherein the first type payload data includesat least one of synchronous, asynchronous, and plesiochronous data. 20.The method of claim 14 wherein the second type payload data includespacket data.
 21. The method of claim 14 wherein the synchronized firsttype payload data and second type payload data is assigned by sequentialbit interleaving.
 22. The method of claim 14 wherein the plural firsttype data sources are synchronized by bit stuffing.